The objective of this study is to determine the chronic toxicity and carcinogenicity of Cobalt Sulfate administered by inhalation to Fisher 344 rats and B6C3F1 mice. The contract will include a Phase I which is the basic award and includes the preliminary atmosphere generation/monitoring effort. Phase 2 consists of a 104-Week Inhalation Study with Fischer F344 rats and B6CF1 mice treating at 3 dose levels plus controls.